Annual report pursuant to Section 13 and 15(d)

Income taxes - Schedule of Components of Income From Continuing Operations before Income Taxes (Details)

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Income taxes - Schedule of Components of Income From Continuing Operations before Income Taxes (Details) - USD ($)
$ in Thousands
12 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2015
Income before income taxes:      
United States $ 257,910 $ 238,871 $ 232,359
Foreign 56,325 47,097 27,460
Income before income taxes $ 314,235 $ 285,968 $ 259,819